In communication networks such as PSTNs or packet-oriented intranet or Internet, a voice memory device can be permanently associated with a terminal. This is done so that a voice message can be left even when the terminal and its associated subscriber cannot be reached. In this configuration, the voice memory—also known as an answering machine—is placed on standby by the subscriber. When a voice memory associated with a terminal is on standby, a call to that terminal activates the voice memory or switches on the answering machine at the subscriber's location, either immediately or after a few rings. After playing a greeting to the calling terminal, the voice memory is placed into a mode in which it can receive and store voice messages from the calling terminal. This type of voice memory can either be assigned to an individual terminal or used in a communication network in such a way that the voice memory is associated with a particular terminal.
If no voice memory is associated with a called terminal, it is currently not possible to transfer a voice message to the called terminal if the called subscriber cannot be reached. In order to inform the called subscriber of the desire to make a connection or exchange voice information, provided that the communication network permits it, an “automatic callback” or “message waiting callback” command feature can be activated. For both of these command features, when the called subscriber is available at his terminal, either a callback to the calling terminal is initiated automatically, provided that the called subscriber's terminal is active, or information is displayed for him indicating that he should call the calling subscriber back. However, a callback resulting from either of these command features can fail again if the subscriber at the terminal that made the original call is not available or cannot be reached. It is currently not possible with either of these command features to transmit a voice message to the called subscriber.